Enhancement of influenza virus hemolysis by physical and serological treatments.

The mode of hemolysis by influenza A virus was compared with that of Sendai virus. The WSN strain of influenza virus grown in either eggs or MDCK cells expressed hardly any hemolytic activity by itself. Treatment of the MDCK cell-grown WSN virus with sonication or freezing and thawing moderately enhanced the hemolytic activity, but the maximum level attainable was considerably lower than that of Sendai virus. A high level of hemolytic activity comparable to that of Sendai virus was obtained only after treatment of the virus with antibody and complement. An electron microscopic study revealed that non- or low-hemolytic WSN virions were not permeable to uranyl acetate stain in contrast with the hemolytic virions obtained after treatment with antibody and complement, indicating that the hemolytic virions had sustained some injury to their envelopes. These phenomena were comparable to those found with Sendai virus, showing that damage to the envelope is also responsible for the hemolysis of influenza virus. The influenza viruses, however, remained spherical after every treatment and the stain did not penetrate into the core of the virion. These observations suggest that the envelope of influenza virus is more rigid than that of Sendai virus but that the hemolytic process of influenza virus is nevertheless mediated through envelope-membrane fusion as in the case of Sendai virus.